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Re: U.S. NRC proposes changes to shallow dose exposure limit
Am I correct in saying that "the effective shallow
dose equivalent (Hs) is the exposure of the skin or an
extremity from external sources of ionizing radiation
at a tissue depth of 7 mg/cm2 averaged over 1 cm2?"
Isn't this definition designed for radiation exposure
from sources which are external to (not in contact
with) the affected tissue?
Paul Shafer
--- Mike Lantz <mlantz33@CYBERTRAILS.COM> wrote:
> I think some of you know that I was on the NCRP
> committee that came up with the
> 10 cm2 limit. I'm very happy with this value for
> hot particles as a limit for
> deterministic effects - especially as it is a
> unified limit of 50 rem for skin.
> There is far too much to talk about over Radsafe, so
> if you want to talk about
> how we came to 10 cm2 and its value, call me at 623
> 393 5200. As an example, 1
> cm2 was never a biological endpoint from hot
> particles - it was equally
> arbitrary as most effects studied on pig
> irradiations were 1-2 mm2 from the
> betas. However, many particles are stepped on and
> attached to shoes - one
> station just encountered this problem. And these
> particles expose larger areas
> than 1 cm2 from the photons.
>
> We discussed and wrote about the stochastic effects
> from hot particles and
> determined them to be negligible, of course.
>
> Mike Lantz, CHP
>
> glen.vickers@EXELONCORP.COM wrote:
>
> > I've been away from skin dose for a couple of
> years, but here are a couple
> > issues I can think of right away.
> >
> > I believe the organ weighting factors assume
> uniform irradiation of the
> > entire organ and that will essentially never be
> the case for skin
> > contamination events.
> >
> > If they're thinking about changing the rules, then
> they need to also think
> > about practical ways to calculate the quantities.
> Right now, if a person
> > had varying levels of contamination on a planar
> source, the tech would take
> > the highest direct reading with a 15.5 cm^2 GM
> probe and we'd calculate that
> > as a 15.5 cm^2 source over a 1cm^2 receptor.
> Some might concentrate that
> > reading as a 1 cm^2 source over a 1 cm^2 receptor,
> but that bumps up the SDE
> > by about a factor of 15 for Co-60. I'd like to
> see some additional guidance
> > about assumptions of the source size, because you
> can't really measure, and
> > activity/probe area. With the new guidance should
> we take the reading/15.5
> > cm^2 and apply that activity/cm^2 as a 10 cm^2
> source over a 10 cm^2
> > receptor? Different approaches yield signficantly
> different answers.
> >
> > Why change to 10 cm? The calculated doses will
> drop significantly. Why not
> > just increase the limit over the same 1 cm^2 if we
> think we are overstating
> > the stochastic risks from planar sources?
> >
> > What about deterministic effects from hot
> particles? The NRC's enforcement
> > guidance stated that a limit of 75 uCi-hr would be
> applied in addition to
> > the 50 rem SDE. NRC (IE 90-48, NCRP 106) Also
> hot particle dose is not
> > SDE, but SD or hot particle dose. The NRC needs
> to codify gudiance for
> > point and planar sources. They did a good job
> with the enforcement
> > guidance, but now would be the time to address the
> issue appropriately.
> >
> > Glen Vickers
> >
> > > -----Original Message-----
> > > From: Sandy Perle [SMTP:sandyfl@EARTHLINK.NET]
> > > Sent: Thursday, July 12, 2001 9:58 AM
> > > To: radsafe@list.vanderbilt.edu
> > > Subject: Re: U.S. NRC proposes changes to
> shallow dose exposure limit
> > >
> > > > This is in keeping with the recommendations
> found in NCRP 130.
> > >
> > > While this proposal is an improvement, the NRC
> needs to move towards
> > > acceptance of dose weighting. The skin, being an
> organ, should be
> > > viewed as other organs are, and where there are
> weighting factor
> > > applied, if the NRC would accept the
> methodology, such as what is
> > > outlined in HPS N13.41-1997.
> > >
> > > In my opinion, it is still unrealistic and not
> logical to assign a
> > > SDE based on the highest 1 cm, 10 cm or whatever
> number of cm's one
> > > wants to consider, when in all practicality, the
> cumulative dose
> > > effect to the person is insignificant. Now, for
> very high dose
> > > particles, I can agree that averaging needs to
> be assessed. However,
> > > for the general population of workers, using the
> highest dose nees to
> > > be re-thought.
> > >
> > >
>
------------------------------------------------------------------------
> > > Sandy Perle
> Tel:(714) 545-0100 / (800)
> > > 548-5100
> > > Director, Technical
> Extension 2306
> > >
> > > ICN Worldwide Dosimetry Service
> Fax:(714) 668-3149
> > >
> > > ICN Pharmaceuticals, Inc.
> E-Mail:
> > > sandyfl@earthlink.net
> > >
> > > ICN Plaza, 3300 Hyland Avenue
> E-Mail: sperle@icnpharm.com
> > >
> > > Costa Mesa, CA 92626
> > >
> > > Personal Website:
> http://www.geocities.com/scperle
> > > ICN Worldwide Dosimetry Website:
> http://www.dosimetry.com
> > >
> > >
>
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